Clamprite Spindle Drawbar Force Gage

Benefits of Measuring Spindle Drawbar Force

The Clamprite Spindle Drawbar Force Gage is the best selling tool for testing the spindle drawbar pull force of CNC Machining Centers. The use of this economical spindle drawbar force checking tool will maximize machine up time and minimize spindle down time costs associated with wear and damage of drawbars, clamping collets, pull studs, toolholders and tool tapers. By measuring the tool clamping force with this gage, spindle repair costs and repair time can be minimized.

Drawbar force is often the first thing to weaken or fail on a CNC Machining Center!

A stack of 100 to 150 Belleville springs provide the retention force that pulls the toolholder into the spindle taper. Belleville springs wear grooves into the drawbar and the friction between these springs and the drawbar can result in drawbar force loss, which can permit chatter, bad finish, reduced cutter life, and scrapped parts. Belleville springs can and do fatigue and break, resulting in extreme loss of drawbar force. Programmers will often compensate for this, unaware that one spring after another is failing.

The toolholder can eventually pull out of the spindle taper during a cut, causing damage to the spindle taper, bearings, toolholder and pullstud, cutter, and fixture. A routine force check with a spindle drawbar force gage would have revealed drawbar force loss, which would be the cue to initiate corrective action.

How to Use the Clamprite Gage

By placing the Clamprite Gage (with an appropriate taper adapter) into the spindle taper, and causing the drawbar to pull on the pullstud (or retention knob) that you have threaded into the internal transfer screw coupling, it takes less than one minute to check the drawbar pull force against the machine manufacturer’s recommended level. The force gauge is simply hydraulic, with no batteries, no cables and no delicate electronics to go wrong. Since the piston surface area is 1 square inch, a pressure gauge converts directly to pounds of force. Many shops use the Clamprite Gage and most say it paid for itself the first time they used it … because they caught a drawbar exerting low force and they corrected it, before that caused a crash and cost a spindle taper regrind (see Spindle Taper Grinding) or a full spindle repair (see Spindle Repair).

When to Use the Clamprite Gage

Most everyone will check drawbar force after a crash has occurred. But if you record of each spindle’s drawbar pull on a routine basis, you may be alerted to drawbar force loss and trends over time and have a faulty drawbar stopped before a crash occurs. The more frequently you check spindle drawbar pull, the sooner a spindle drawbar force loss is detected.

To order your spindle drawbar force gage – Call: 519 671 3911 or, use the form or our email address, at the bottom-right of any webpage!

Clamprite Gage Kits provide an easy, accurate and economical means of measuring tool clamping force. Kits are furnished in a foam fitted metal tool box and include the gagehead, a spindle adapter, and an internal transfer screw coupling to accept all pull studs. You use your own pull stud or retention knob. The Clamprite Gage Kits include a Certificate of Accuracy traceable to NIST (National Institute of Standards and Technology).

The universal gagehead will fit to adapters for the various spindle tapers:

How to order a Clamprite Spindle Drawbar Force Gage

Select a gagehead with sufficient capacity to measure your highest drawbar pull. Select a spindle taper adapter for each size and type of taper in your plant. Or, select a kit consisting of a gagehead and spindle taper adapter(s). Order additional adapters as needed below:

Spindle Drawbar Force Gageheads

Model/Part Number

Description

Price (US Dollars)

CG3K

3,000 lb. Gagehead

$679.00

CG5K

5,000 lb. Gagehead

$679.00

CG10K

10,000 lb. Gagehead

$719.00

CG15K

15,000 lb. Gagehead, Series II

$989.00

CAT Spindle Adapters

CAT adapters include a Transfer Screw Coupling which accepts all standard Inch pull studs. You use your own pull stud.

Model/Part Number

Description

Price (US Dollars)

CA30C

CAT 30 Adapter

$139.00

CA40C

CAT 40 Adapter

$149.00

CA45C

CAT 45 Adapter

$159.00

CA50C

CAT 50 Adapter

$169.00

CA60C

CAT 60 Adapter

$569.00

BT Spindle Adapters

BT adapters include a Transfer Screw Coupling which accepts all standard Metric pull studs. You use your own pull stud.

Model/Part Number

Description

Price (US Dollars)

CA30B

BT 30 Adapter

$139.00

CA35B

BT 35 Adapter

$142.00

CA40B

BT 40 Adapter

$149.00

CA45B

BT 45 Adapter

$159.00

CA50B

BT 50 Adapter

$169.00

CA60B

BT 60 Adapter

$569.00

ISO Spindle Adapters

ISO adapters include a Transfer Screw Coupling which accepts all standard ISO pull studs. You use your own pull stud.

Model/Part Number

Description

Price (US Dollars)

CA30I

ISO 30 Adapter

$139.00

CA40I

ISO 40 Adapter

$149.00

CA45I

ISO 45 Adapter

$159.00

CA50I

ISO 50 Adapter

$169.00

CA60I

ISO 60 Adapter

$569.00

Capto Spindle Adapters

Model/Part Number

Description

Price (US Dollars)

CAPTO 03

Capto C3 Adapter

$435.00

CAPTO 04

Capto C4 Adapter

$459.00

CAPTO 05

Capto C5 Adapter

$489.00

CAPTO 06

Capto C6 Adapter

$595.00

CAPTO 08

Capto C8 Adapter

$789.00

CAPTO 06

Capto C6 Adapter, for 15,000 lb. gagehead, Series II

$695.00

CAPTO 08

Capto C8 Adapter, for 15,000 lb. gagehead, Series II

$889.00

Kennametal KV Spindle Adapters, Kennametal KM Spindle Adapters

Model/Part Number

Description

Price (US Dollars)

KV4540

KV 4540 Adapter

$639.00

KV5045

KV 5045 Adapter

$719.00

KM32

KM 32 Adapter

$625.00

KM63

KM 63 Adapter

$829.00

KM80

KM 80 Adapter

$1295.00

Monarch Spindle Adapters

Model/Part Number

Description

Price (US Dollars)

M6045

Monarch 45 Adapter

$549.00

New Century Spindle Adapters

Model/Part Number

Description

Price (US Dollars)

NC5-46

NC5-46 Adapter

$619.00

NC5-63

NC5-63 Adapter

$629.00

HSK Spindle Adapters

Note: HSK spindles must have at least 75% of their specified drawbar force to stretch the arbor over the spindle nose and fully seat the arbor flat against the face. HSK spindles need to be checked frequently to ensure adequate drawbar force.

Model/Part Number

Description

Price (US Dollars)

CHSK E25

HSK E-25 Adapter

$399.00

CHSK E32

HSK E-32 Adapter

$419.00

CHSK A40

HSK A-40 Adapter

$439.00

CHSK A50

HSK A-50 Adapter

$469.00

CHSK A50

HSK F-63 Adapter

$469.00

CHSK A63

HSK A-63 Adapter

$489.00

CHSK A80

HSK A-80 Adapter

$679.00

CHSK A100

HSK A-100 Adapter

$849.00

CHSK A125

HSK A-125 Adapter

$989.00

CHSK A100

HSK A-100 Adapter, for 15,000 lb. gagehead, Series II

$974.00

CHSK A125

HSK A-125 Adapter, for 15,000 lb. gagehead, Series II

$1114.00

CAT Spindle Drawbar Force Gage Kits (Gagehead and one or two Spindle Adapters)

Model/Part Number

Description

Price (US Dollars)

CG3K30C

3,000 lb gagehead including CAT 30 taper adapter

$819.00

CG3K40C

3,000 lb gagehead including CAT 40 taper adapter

$829.00

CG5K40C

5,000 lb gagehead including CAT 40 taper adapter

$829.00

CG5K50C

5,000 lb gagehead including CAT 50 taper adapter

$849.00

CG10K50C

10,000 lb gagehead including CAT 50 taper adapter

$885.00

CG5K40/50C

5,000 lb gagehead including CAT 40 & 50 adapters

$989.00

CG10K40/50C

10,000 lb gagehead including CAT 40 & 50 adapters

$1025.00

BT Spindle Drawbar Force Gage Kits (Gagehead and one or two Spindle Adapters)

Frequently Asked Questions

1) I have various machines with drawbar retention force specifications up to 4600 Lbs. Can I use the 5000 PSI pressure gage for all the smaller, lower force machines?

Yes. However, reading the numbers on the 3000 PSI pressure gage is easier than on a 5000 PSI pressure gage because there are fewer numbers on the dial. But a slight difference in reading accuracy is not that important because there is little concern about 10 or 20 Lbs — or even 100 Lbs. The real concern
is when a machine is 20% – 30% low on drawbar force. Spindle technicians usually accept 10% variation when rebuilding a drawbar.

2) What about the accuracy of the Clamprite Drawbar Force Gage versus the higher priced electronic and digital drawbar force gages? It is mentioned how the digital are “extremely accurate” in your sales brochure. Isn’t it better to have high accuracy when available?

Yes … and no! More accuracy is good when FREE. We believe the electronic gages with digital display are overkill for the shop floor in terms of accuracy and cost. The extremely accurate and expensive digital drawbar force check gages are similar to what we use to certify the Clamprite Gage. Our accurate and rugged tool clamping force gage is better suited to a shop environment where the delicate electronic spindle drawbar force gages can be easily damaged. If a Clamprite Drawbar Force Gage is dropped, a pressure gage could cost $40. A digital gage can cost over $1,000 to repair. So … our Spindle Drawbar Force Gage can be purchased new for less than the repair cost of an electronic spindle drawbar force checking gauge with digital display. The Clamprite Gage Kit includes a Certificate of Accuracy traceable to National Institute of Standards and Technology (NIST). These digital drawbar force check gages are sometimes called a spindle drawbar dynamometer. Unfortunately, they neither measure power nor the two components of power … rotational speed and torque. In fact, for safety reasons, there can be no spindle rotation while doing the pull force check. These spindle check gages simply measure the drawbar axial pull force … there is no power check and a spindle drawbar force gage is not a spindle dynamometer.

3) My CNC Mill has a high speed HSK type spindle. Can I use the same gage head to test this
machine?

Yes, the gage head used for testing the common long taper spindles is the same for testing the HSK spindle system. An HSK adapter is required for HSK spindle testing. These HSK adapters are available for all HSK spindle sizes and are accurate, durable and low in cost.

HSK spindles must be tested frequently to assure that they are within 75% of spec at all times. The tool holders will not seat correctly to the face if the drawbar is pulling less than 75% of spec.

We highly recommend to anyone who sells, uses, or services HSK machinery or tooling that you read the “HSK Handbook”. It is well written (by Dr. E. Kocherovsky) and not only tells the history of HSK and it’s full story, it also has about 150 excellent color charts, graphs, and pictures explaining how it works. There is even a complete set of blueprints for each size of spindles and arbors. The contents of the book will amaze you, and make you glad that your shop is not making HSK tooling!! It is well worth it’s price. Our price is only $149 when you purchase a gage kit.

4) I can’t find the specified drawbar force for my machine anywhere in the manuals. Can you tell me what the drawbar force my machine should provide?

There are so many variations, even among similar machines. Only the manufacturer can say for
sure. Some general figures are: 1800 to 2500 Lbs for most 40-taper spindles, 3800 to 4800 Lbs for most
50-taper spindles except heavy-duty versions which may be considerably higher. This is only a
reference, and not a guide for any specific machine or spindle. To obtain the specific force for any
particular machine, get the model number, the serial number, and date it was built from the nameplate
and consult the factory representative.

5) What is the difference between using a standard tool holder as the spindle adapter vs. using the specially designed Clamprite Spindle Adapters?

A standard end mill holder can be used as the interface for drawbar testing. Our Adapters cost less
than most tool holders, and since there are no tool changer flanges, the 50 taper (one unit) adapter
fits all CAT, BT, and ISO spindles. Finding the right holder can be time consuming because it is often
back in use on a machine when it is needed.

But the best reason to use a Clamprite Spindle Adapter is because we have found tool holders to be
out of tolerance to the gage line dimension of the spindle. In fact, some tool holders (from reputable
manufacturers) were .0125 over the high tolerance limit. Some were nearly that amount below the low
tolerance limits. This amount of variation can cause great differences in spindle drawbar force
readings.

All Clamprite Spindle Adapters are inspected with spindle taper gages to verify gage-length
accuracy. A spindle that has .001 wear on the surface will allow a tool to seat .0069 deeper into the
spindle pocket — well past the gage-line tolerance limits, and enough to cause reduced overall drawbar
holding force!

6) I have a 50-taper spindle on a geared head machine designed for cutting steel. Can I use the 5000 PSI pressure gauge to test it?

Most 50-taper machines are below 5000 PSI, usually from 3800 to 4800 PSI. But some heavy duty
50-taper machines can go to 7800, or more. If you over pressure the gauge, it may become inaccurate.
See precautions in the instruction manual. As a courtesy to our customers, Clamprite will replace a
pressure gauge with another gauge at no labor cost, if shipping is prepaid both ways. The complete
re-certifying procedure is done for a nominal fee of just $59.95 (includes certificate traceable to
NIST).

7) One of our machines is very large and was designed for heavy duty use. Someone said it may provide over 10,000 Lbs of drawbar force. Can the CG be used to test its drawbar?

The Clamprite Gage II is a heavy duty version of the standard Clamprite Drawbar Force Gage. The
standard Clamprite Drawbar Force Gage will test up to 10,000 Lbs when fitted with the proper pressure
gauge. The Clamprite Gage II will test up to 15,000 Lbs. Contact us for testing of forces over 15,000
Lbs. If you attempt to test the spindle and it is over 10,000 Lbs, the 10,000 PSI pressure gauge may be
ruined and hydraulic fluid may squirt out causing injury. See precautions in the Instruction Manual.
Your gage head can be re-fitted with a higher reading pressure gauge at no charge if courier
charges are paid both ways. There is a nominal charge for re-certification, recording and issuing a
new Certificate of Accuracy traceable to NIST ($59.95).

8) Can a Clamprite Drawbar Force Gage fitted with a 10,000 PSI pressure gauge be used to test spindle with 2000 Lbs of force?

Yes, but reading a 3000 PSI gauge is slightly easier than reading a 10,000 PSI gauge because there
are fewer numbers on the face of the pressure gauge but the 10,000 PSI gauge will show you the drawbar
force that your machine is producing. Changing gauges should only be done by qualified hydraulic repair
personnel. As a courtesy to our customers, Clamprite will replace a gauge with another one of
different pressure at no charge, except for the gauge and re-certification. Labor is free. Use caution
if you attempt replacement yourself, as the fluid can squirt out and cause skin irritation, and
improper bleeding of the gauge and body may cause false readings. Also, commercial gauges can vary
greatly in accuracy. Clamprite uses only high accuracy stainless steel pressure gauges, and we also
test and certify each assembly for accuracy on a certified electronic test bench.

9) We are a small shop with no customer requirements to verify our drawbar force. How long can we go without checking or re-certifying the Clamprite Spindle Drawbar Force Gage?

A lot of attention is being given to machine condition today. Some companies, especially aerospace,
are even condition-coding machines and requiring accuracy tests such as “ball-bar testing” to be
performed by vendors before parts can pass QC requirements. It is just a matter of time before they
realize that a drawbar is just as critical for consistent machining as the axis drives and ball screw
condition. But under your circumstances, you might go a few years without worrying about the gauge
accuracy. If the Clamprite Drawbar Force Gage is not over-pressured, it should remain accurate for many
years. However, Clamprite will check the accuracy of your gauge for free as long as you own it, if
shipping is paid both ways. We do not record and issue a new Certificate of Accuracy when doing a free
courtesy check. But it will verify that your gage is still in the original condition. There is a
nominal fee of $59.95 for a complete re-certification.

10) My machine uses hydraulic pressure to hold the tools in the spindle. Will the Clamprite
Drawbar Force Gage work for this application?

Yes. Whatever the means of creating tool retention force, that force can be measured with the Clamprite Gage.

However, there is some confusion about this. Nearly all machines use the spring stack method of tool
retention . But the method of releasing the tool from the spring pressure comes from a hydraulic
piston which is usually energized by an air cylinder. Compressed air is supplied to the
air-over-hydraulic piston (usually located on top of the spindle) which acts like a small jack-type
press for compressing the spring stack which in turn releases the clamping force acting on the tool
holder’s pull-stud. Sounds a little complicated, but is actually fairly simple once you have seen all
the parts laid out. Sometimes people are confused about how the hydraulics work. The
air-over-hydraulic piston can be heard during a tool change, but it is usually used to release the
tools, not to hold them.

11) In advertising and in your Instruction Sheet you spell the word gauge as simply “gage” at times. Why the difference?

Gage (spelled this way) is somewhat traditional in the metal working trades, except when
specifically discussing a pressure gauge. The bourdon-tube type of pressure gauge has come to be known
as simply “a gauge“, whereas many other gages (like radius gages, depth gages, etc.) are more like a
method of measuring. Most tool making companies like the L.S. Starrett Co. for example, still use the
older spelling of gage when describing their products. Most dictionaries list both spellings as
acceptable.

12) You used to offer an adapter to test drawbar force on a Bridgeport mill. Why test drawbar force on a manual machine?

The Bridgeport Adapter was designed to give people a way to see and feel the kind of force that can be generated simply by turning a screw with a wrench. Most people are surprised when they use the Clamprite Gage on a Bridgeport type mill. It showed that most people applied twice the tool holding force than most 40-taper CNC Machining Centers when they are new! It was a real eye opener and a lot of fun, and it might have saved some Bridgeports from damage.

To order your spindle drawbar force gage – Call 519-671-3911, or click haviland@precisionspindleinc.com or Contact Us in the footer below or the header above for more information!